Distance measuring apparatus and distance measuring method

ABSTRACT

A distance measuring apparatus ( 11 ) optically detects a measuring target, thereby measuring an object distance, which is the distance to the measuring target. The orientation of an optical axis of a lens is set to be different from an advancing direction of light incident from the measuring target. The lens is configured to form an image from the incident light, thereby obtaining an image of the measuring target. The distance measuring apparatus includes an imaging relative quantity calculating means ( 31, 32 ) for obtaining an imaging position indicative of a position of the image with respect to the lens for each of a plurality of wavelengths possessed by the incident light, thereby calculating an imaging relative quantity, which is a quantity indicative of a relative relationship between the imaging positions; storage means ( 17 ) for storing correlation information ( 18 ), which is information determined by a chromatic aberration characteristic of the lens and the orientation of the optical axis in order to indicate a correlation between the imaging relative quantity and the object distance; and distance calculating means ( 33 ) for calculating the object distance by checking the imaging relative quantity against the correlation information ( 18 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application of InternationalApplication No. PCT/JP2010/062404, filed Jul. 23, 2010, the contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a distance measuring apparatus formeasuring distance to a measuring target present in the surroundingenvironment, particularly, a measuring target present in a trafficenvironment based on optical detection of the measuring target, and to adistance measuring method that is suitably for use in the distancemeasuring apparatus.

BACKGROUND ART

Conventionally, a distance measuring apparatus has been put intopractical use to measure the distance to a measuring target. Theapparatus measures the distance to a measuring target based on opticaldetection of light selected from visible and invisible light. Thedistance measuring apparatus is provided on a vehicle, which is amovable body, for example, in order to measure the distance (relativedistance) between another vehicle, which is a measuring target or thelike, and a host vehicle (the distance measuring apparatus itself). Thedistance measuring apparatus offers information about the distance thusmeasured as driving support information to a driving support apparatusor the like, for example, for supporting avoidance of a collision withother vehicles.

There are known distance measuring apparatuses for optically measuringdistance to a measuring target, which are described in Patent Document 1and Patent Document 2.

The distance measuring apparatus described in Patent Document 1 has alight source for projecting light formed in a predetermined patternhaving different wavelengths from each other onto a measuring target andpicks up an image of a pattern of the light projected onto the measuringtarget in a different direction from the optical axis of the lightsource. The distance measuring apparatus measures the distance to themeasuring target based on a change in the pattern of the projected lightand the pattern of the light subjected to the image pickup. Thus, thedistance measuring apparatus described in Patent Document 1 needs tohave a light source for projecting onto the measuring target, lighthaving sufficient intensity for enabling the image pickup. For thisreason, when the distance measuring apparatus described in PatentDocument 1 is provided on a vehicle, the light source is to project alight pattern having such an intensity as to enable the image pickuponto a measuring target, which is placed apart from the host vehicle byseveral tens to several hundreds meters in some cases. In other words,the quantity of the energy consumed by the light source cannot bedisregarded.

On the other hand, Patent Document 2 discloses a distance measuringapparatus using no light source. The distance measuring apparatusincludes two cameras, that is, a camera that is sensitive to a visiblespectral range and a camera that is sensitive to an infrared spectralrange. The cameras are disposed at a predetermined intervaltherebetween. The distance measuring apparatus measures the distance toan identical measuring target by applying a triangulation method to animage of the measuring target, which is picked up by the respectivecameras. Thus, the distance measuring apparatus described in PatentDocument 2 does not need a special light source. For this reason, theenergy consumption is admittedly low. In order to maintain highprecision in the measurement of the distance, it is indispensable toaccurately maintain the predetermined interval between the two cameras,which is the basis of the triangulation method.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2002-27501-   Patent Document 2: Japanese National Phase Laid-Open Patent    Publication No. 2007-506074

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, a distance measuring apparatus provided on a vehicle isinfluenced by vibration or distortion of a vehicle body, or the like.For this reason, it is not easy to maintain a predetermined intervalbetween two cameras attached to the vehicle body with high precision. Ina case in which the distance measuring apparatus is particularlyprovided on the vehicle, thus, there is room for further improvement inpractice in respect of a simplification of the structure or the like.

In consideration of the actual circumstances, it is an objective of thepresent invention to provide a distance measuring apparatus capable ofmeasuring a distance to a measuring target with a simple structure evenif the distance measuring apparatus is provided on a vehicle or thelike, and a distance measuring method that is suitably used in thedistance measuring apparatus.

Means for Solving the Problems

To achieve the foregoing objective, the present invention provides adistance measuring apparatus for measuring distance to a measuringtarget by optically detecting the measuring target. The apparatusincludes a lens, an imaging relative quantity calculating means, astorage means, and a distance calculating means. The lens has an opticalaxis in a different orientation from an advancing direction of lightincident from the measuring target. The lens is configured to form animage from the incident light, thereby obtaining an image of themeasuring target. The imaging relative quantity calculating meanscalculates an imaging relative quantity by obtaining an imaging positionindicative of the position of the image with respect to the lens foreach of a plurality of wavelengths possessed by the incident light. Theimaging relative quantity is a quantity indicative of a relativerelationship between the imaging positions. The storage means storescorrelation information, which is information determined by a chromaticaberration characteristic of the lens and the orientation of the opticalaxis in order to indicate a correlation between the imaging relativequantity and the object distance. The distance calculating meanscalculates the object distance by checking the imaging relative quantityagainst the correlation information.

According to the structure, the lens having the optical axis in thedifferent orientation from the advancing direction of the incident lightis used so that the imaging positions for the respective wavelengths aredifferent from each other. Consequently, the imaging relative quantitiesbetween the imaging positions are detected to be different from eachother. In other words, the distance measuring apparatus can measure thedistance to the measuring target based on the imaging relativequantities, which are different from each other. An ordinary lens has arefractive index that is varied for each wavelength of the light, thatis, causes a chromatic aberration. For this reason, the imaging positionis varied for each wavelength when an image of the light having thewavelengths is to be formed. In a case in which the optical axis of thelens is inclined with respect to the advancing direction of the incidentlight, accordingly, the lens refracts the incident light to be inclinedtoward the orientation of the optical axis of the lens. Thus, the lightis refracted in a refractive index for each wavelength so that theimaging positions of the light are different from each other in adirection perpendicular to the advancing direction of the incident light(a horizontal direction or a vertical direction of the lens) for eachwavelength. On the other hand, the object distance, which is thedistance between the lens and the measuring target is varied withrespect to a longitudinal direction of the lens so that an incidentangle of the light on the lens is made different. For this reason, theobject distance is varied so that an imaging position of light of asingle wavelength is also changed. Consequently, the distance measuringapparatus can measure the distance to the measuring target based on arelative relationship between the imaging positions for the respectivewavelengths.

Moreover, the imaging positions for the respective wavelengths aredifferent from each other in the direction perpendicular to theadvancing direction of the incident light. Therefore, the lights havingthe respective wavelengths are subjected to imaging without a hindranceto a detection over a common imaging plane which is generally providedto face the lens. Consequently, the imaging plane can detect the imagingpositions for the respective wavelengths. In other words, it is rarelynecessary to move the imaging plane in order to detect the imagingposition. For this reason, an apparatus for moving the imaging plane isnot required, for example. In other words, the imaging positions for therespective wavelengths can be detected with a simple structure.

In addition, it is possible to obtain the difference between the imagingpositions for the respective wavelengths based on the chromaticaberration by detecting the imaging positions for the respectivewavelengths through a common lens (optical system). Consequently, thedistance can be measured by means of a single optical system, that is, asingle camera. Therefore, as compared with a case in which a pluralityof cameras is used, for example, the flexibility for the arrangement ofthe camera is increased. Furthermore, it is not necessary to maintainthe arrangement position of the camera with high precision. Thus, it ispossible to simplify the structure of the distance measuring apparatus.

Furthermore, an ordinary lens is subjected to chromatic aberrationcorrection and is often configured in such a manner that the imagingdistances for the respective wavelengths are coincident with each otherfor only light of the wavelengths to be acquired, for example, onlylight having a red wavelength, a blue wavelength and a green wavelengthfor an image. With the structure, however, light having a wavelengththat is not subjected to chromatic aberration correction can be used forthe measurement of the distance. Therefore, it increases the flexibilityfor the selection and design of the wavelength to be used in thedistance measuring apparatus. In addition, it increases the flexibilityfor the selection and design of the optical system to be employed forthe distance measuring apparatus.

The light preferably has two wavelengths, in which the imaging positionsare different from each other, and the correlation informationpreferably constitutes map data, in which the imaging relativequantities are caused to correspond to the object distances,respectively.

According to the structure, the distance measuring apparatus can measurethe distance to the measuring target based on the lights having twowavelengths in which the imaging positions through the lens aredifferent from each other. If the light has two wavelengths or more,thus, the distance measuring apparatus can measure the distance to themeasuring target. Therefore, it is possible to easily carry out themeasurement of the distance.

The imaging relative quantity may be an imaging position difference,which is the difference between the imaging positions for the twowavelengths.

According to the structure, the imaging relative quantity is detected asthe difference between the imaging positions of the light having twowavelengths. Therefore, it is possible to easily carry out a calculationrelated to the detection.

The imaging relative quantity may be an imaging position ratio, which isthe ratio of the imaging positions for the two wavelengths.

According to the structure, similarly, it is possible to easily carryout the calculation related to the detection.

The optical axis of the lens may be inclined with respect to theadvancing direction of the incident light.

According to the structure, if the optical axis of the lens is inclinedwith respect to the incident light, a difference is made between theimaging positions for the respective wavelengths. The distance measuringapparatus can measure the distance to the measuring target based on thedifference between the imaging positions. For example, in the case of ageneral convex lens, if the lens is disposed with an inclination to theadvancing direction of the incident light, the optical axis of the lensis inclined with respect to the advancing direction of the incidentlight. Thus, it is possible to simplify the arrangement or mode of thelens in the distance measuring apparatus or the characteristic of thelens.

A surface of the lens may be non-rotationally symmetrical with respectto the optical axis of the lens.

According to the structure, it is possible to incline the optical axisof the lens by forming the surface of the lens to be non-rotationallysymmetrical with respect to the optical axis of the lens. By regulatingthe surface shape of the lens, accordingly, it is possible to inclinethe optical axis of the lens in order to meet a wavelength of an emittedlight and distance to a measuring target. Therefore, it increases theflexibility of the selection and a design of the lens to be used in thedistance measuring apparatus.

A refractive index of the lens may be non-rotationally symmetrical withrespect to the optical axis of the lens.

According to the structure, it is possible to regulate the inclinationof the optical axis of the lens by causing the refractive index of thelens to be non-rotationally symmetrical with respect to the opticalaxis. Accordingly, it is possible to incline the optical axis of thelens in order to meet the wavelength of the emitted light and thedistance to the measuring target. Consequently, it also increases theflexibility of the selection and design of the lens to be used in thedistance measuring apparatus.

The lens is preferably a part of a spectrum sensor for detecting lighttransmitted from the measuring target.

According to the structure, it is possible to detect light having aplurality of optional wavelengths by using the spectrum sensor.Therefore, it is possible to calculate a large number of imagingrelative quantities based on the imaging positions of the images formedby the lights having the detected wavelengths. By measuring a distancebased on the large number of imaging relative quantities, it is possibleto enhance precision in the measurement of the distance. Moreover, thespectrum sensor originally has a high flexibility of the selection ofthe wavelength. Consequently, it is also easy to properly select lightof a suitable wavelength for the measurement of the distance dependingon a surrounding environment, an environmental light or the like.Furthermore, the spectrum sensor can detect lights having a plurality ofwavelengths in the first place. Therefore, the distance measuringapparatus can be configured simply. In other words, the existingspectrum sensor can be used as the distance measuring apparatus.

To achieve the foregoing objective, the present invention also provideda distance measuring method for measuring distance to a measuring targetby optically detecting the measuring target. The method includes: animaging position calculating step for forming an image of the measuringtarget by means of a lens having an optical axis in a differentorientation from an advancing direction of light incident from themeasuring target and obtaining an imaging position indicative of theposition of the image with respect to the lens for each of a pluralityof wavelengths possessed by the incident light; an imaging relativequantity calculating step for calculating an imaging relative quantity,which is a quantity indicative of a relative relationship between theimaging positions; and a distance calculating step for calculating theobject distance by checking the imaging relative quantity againstcorrelation information, which is information determined by the imagingrelative quantity, a chromatic aberration characteristic of the lens,and the orientation of the optical axis in order to indicate acorrelation between the imaging relative quantity and the objectdistance.

According to the method, the imaging positions for the respectivewavelengths are made different from each other through the lens havingan optical axis in a different orientation from the advancing directionof the incident light. Based on the imaging positions for the respectivewavelengths, the imaging relative quantities between the imagingpositions are detected to be different from each other. In other words,the distance measuring method can measure the distance to the measuringtarget based on the imaging relative quantities, which are differentfrom each other. An ordinary lens has a refractive index that is variedfor each wavelength of the light, that is, causes a chromaticaberration. For this reason, the imaging position is varied for eachwavelength when an image of the light having the wavelengths is formed.In a case in which the optical axis of the lens is inclined with respectto the advancing direction of the incident light, accordingly, the lensrefracts the incident light to be inclined toward the orientation of theoptical axis. Thus, the light is refracted in a refractive index foreach wavelength. Therefore, the imaging positions of the light for therespective wavelengths are different from each other in a directionperpendicular to the advancing direction of the incident light (ahorizontal direction or a vertical direction of the lens). On the otherhand, the object distance to be the distance between the lens and themeasuring target is varied with respect to a longitudinal direction ofthe lens so that an incident angle of the light on the lens is madedifferent. For this reason, the object distance is varied so that animaging position of a single wavelength light is also changed. Accordingto the distance measuring method, consequently, the distance to themeasuring target is measured based on a relative relationship betweenthe imaging positions for the respective wavelengths.

Moreover, the imaging positions for the respective wavelengths aredifferent from each other in the direction perpendicular to theadvancing direction of the incident light. The imaging plane isgenerally provided to face the lens and light having the respectivewavelengths is subjected to imaging without a hindrance to detectionover the common imaging plane. Consequently, the imaging plane candetect the imaging positions for the respective wavelengths. In otherwords, it is rarely necessary to move the imaging plane in thelongitudinal direction of the lens in order to detect the imagingposition. For this reason, an apparatus for moving the imaging plane isnot required. In other words, the distance measuring method can detectthe imaging positions for the respective wavelengths with a simplestructure.

Furthermore, the distance measuring method obtains the differencebetween the imaging positions for the respective wavelengths based onthe chromatic aberration on the basis of the imaging positions for therespective wavelengths that are detected by a common lens, that is, acommon optical system. Consequently, a distance can be measured by meansof a single optical system, that is, a single camera. Therefore, ascompared with a method in which a plurality of cameras is used, forexample, it increases the flexibility of the arrangement of the camerain an apparatus employing the distance measuring method.

In addition, an ordinary lens is often subjected to chromatic aberrationcorrection. In other words, the ordinary lens is often configured insuch a manner that the imaging distances for the respective wavelengthsare coincident with each other for only light having wavelengths to beacquired, for example, only lights having a red wavelength, a bluewavelength and a green wavelength for an image. With the distancemeasuring method, however, light of a wavelength that is not subjectedto chromatic aberration correction can be used for the measurement ofthe distance. Therefore, it increases the flexibility for selection anddesign of a wavelength to be used in the distance measuring method. Inaddition, it also increases the flexibility for selection and design ofan optical system in an apparatus employing the distance measuringmethod.

The incident light may have two wavelengths, and the imaging positioncalculating step may obtain the imaging position for each of the twowavelengths. The distance calculating step may acquire the correlationinformation from map data, which causes the imaging relative quantity tocorrespond to the object distance.

According to the method, it is possible to measure the distance to themeasuring target based on light having two wavelengths in which theimaging positions are different from each other. If the light iscomposed of two wavelengths or more, thus, the distance measuring methodcan measure the distance to the measuring target. Therefore, it ispossible to easily carry out the measurement of the distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a system structure of a movable bodyprovided with a spectrum measuring apparatus, which is a distancemeasuring apparatus according to one embodiment of the presentinvention;

FIG. 2 is a schematic diagram showing the structure of an optical systemused in the spectrum measuring apparatus illustrated in FIG. 1.

FIGS. 3(a) to 3(c) are schematic diagrams showing an imaging position inwhich the optical system in FIG. 2 forms an image of a measuring target,where: 3(a) is a diagram showing an imaging position in a case in whichthe measuring target is distant; 3(b) is a diagram showing an imagingposition in a case in which the measuring target is closer to a lensthan that in the case of 3(a); and 3(c) is a diagram showing an imagingposition in a case in which the measuring target is closer to the lensthan that in the case of 3(b);

FIGS. 4(a) and 4(b) are schematic diagrams illustrating a mode in whichthe optical system of FIG. 2 projects an identical measuring target ontoan imaging plane with lights having different wavelengths from eachother;

FIG. 5 is a graph showing the relationship between a shift amountdetected by the spectrum measuring apparatus in FIG. 1 and the distanceto the measuring target;

FIG. 6 is a flowchart showing a procedure for measuring a distance bythe spectrum measuring apparatus in FIG. 1;

FIG. 7 is a schematic diagram showing the structure of an optical systemof a spectrum measuring apparatus, which is a distance measuringapparatus according to another embodiment of the present invention; and

FIG. 8 is a schematic diagram showing the structure of an optical systemof a spectrum measuring apparatus, which is a distance measuringapparatus according to a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 6 illustrate a spectrum measuring apparatus 11, which is adistance measuring apparatus according to an embodiment of the presentinvention. In particular, FIGS. 1 to 5 show the system structure of thespectrum measuring apparatus 11 and FIG. 6 shows a flowchart. FIG. 1 isa block diagram showing a system structure of the spectrum measuringapparatus 11 provided on a vehicle 10, which is a movable body.

In recent years, a technique has been considered to be put intopractical use that recognizes a measuring target present in asurrounding environment of a spectrum sensor based on multispectral dataincluding an invisible light range measured by the spectrum sensor andoffers various supports to a driver depending on the recognizedmeasuring target or the state of the measuring target. For example, adriving support apparatus on a vehicle such as an automobile has beenconsidered that recognizes pedestrians, other vehicles or the like,which are present in the traffic environment around the vehicle based onspectral data measured by the spectrum sensor provided on the vehicle inorder to support driving operation or decision making by the driver.

In order to support a driver operating a movable body such as a vehicle,moreover, information indicative of the relative position of a measuringtarget with respect to the movable body is indispensable for support toavoid or prevent collision of the movable body with other objects, forexample. Therefore, some vehicles are conventionally provided with adistance measuring apparatus for measuring the relative position of ameasuring target with respect to the vehicle itself, and the apparatusesdescribed in Patent Document 1 and Patent Document 2 are known asdistance measuring apparatuses. In a case in which a spectrum measuringapparatus and a distance measuring apparatus are individually providedin a vehicle, however, there is a drawback caused in that an areaoccupied by these apparatuses in the vehicle is increased, the structureof the overall vehicle is made more complex or cost is increased.Therefore, there is a demand to simplify the system structure obtainedby the sensors. For this reason, in the present embodiment, the spectrummeasuring apparatus can be used as a distance measuring apparatuscapable of measuring distance between the distance measuring apparatusitself and the measuring target with a simple structure even if it isprovided on a vehicle or the like.

The spectrum measuring apparatus 11 shown in FIG. 1 has such a structureso as to acquire light information including visible and invisible lightfrom outside of the vehicle, thereby enabling recognition of a measuringtarget and enabling measurement of the distance between the spectrummeasuring apparatus 11 itself and the measuring target. Furthermore, thevehicle 10 includes a human machine interface 12 for transmitting therecognition information, the distance information or the like outputfrom the spectrum measuring apparatus 11 to a passenger of the vehicle10, and a vehicle control device 13 for reflecting the recognitioninformation, the distance information or the like output from thespectrum measuring apparatus 11 on the control of the vehicle. Thespectrum measuring apparatus 11 recognizes a measuring target by a knownmethod. In the present embodiment, therefore, redundant explanation fora structure of a portion of the spectrum measuring apparatus 11 whichserves to recognize a measuring target, a portion of a recognitionprocessing for recognizing the measuring target or the like will beomitted for convenience.

The human machine interface 12 transmits a vehicle condition or the liketo a passenger, particularly, a driver through light, colors, sound orthe like. In other words, the human machine interface 12 is a knowninterface device provided with an operating device such as a push buttonor a touch panel in order to input the intention of a passenger througha button or the like.

The vehicle control device 13, which is one of various control devicesprovided on the vehicle 10 is interconnected to other various controldevices such as an engine control device provided similarly on thevehicle directly or indirectly through an on-vehicle network or the likein order to enable a mutual transmission of necessary information. Inthe present embodiment, when information about the measuring targetrecognized by the spectrum measuring apparatus 11 or information such asa distance to the measuring target is input from the spectrum measuringapparatus 11, which is connected thereto, the vehicle control device 13transmits the same information to the other various control devices.Furthermore, the vehicle control device 13 has such a structure so as toexecute required driving support in the vehicle 10 depending on therecognized measuring target and the distance to the measuring target.

As shown in FIG. 1, the spectrum measuring apparatus 11 includes aspectrum sensor 14 for detecting spectral data R0 of observed light,which is light obtained by observing a measuring target, and a spectraldata processing device 15 for receiving the spectral data R0 from thespectrum sensor 14 and processing the spectral data R0.

The spectrum sensor 14 is configured to generate the spectral data R0 ofthe observed light by detecting a spectral image of the observed light.A plurality of pixels constituting the spectral image has individualspectral data, respectively.

The spectrum sensor 14 has a function for dispersing observed light,which is light including visible and invisible light, into predeterminedwavelength bands. The spectral data R0 output from the spectrum sensor14 has wavelength information, which is information indicative of awavelength forming respective wavelength bands after the dispersion, andlight intensity information, which is information indicative of lightintensity of the observed light for each of the wavelengths of thewavelength bands. The spectrum sensor 14 according to the presentembodiment previously selects 400 nm (nanometers) as a first wavelength(λ1) to be used for measuring a distance, that is, a short wavelength,and selects 800 nm as a second wavelength (λ2), which is longer than theshort wavelength, that is, a long wavelength. In other words, thespectral data R0 includes spectral data configured by light of 400 nmand spectral data configured by light of 800 nm. Moreover, the spectrumsensor 14 also has a function for regulating observed light according toa predetermined wavelength band.

As shown in FIG. 2, the spectrum sensor 14 includes a lens 20 forimaging incident light L and a detecting device 21 for detecting thelight subjected to the imaging through the lens 20. Furthermore, thespectrum sensor 14 includes a filter (not shown) for generating theincident light L from observed light. In other words, the filteraccording to the present embodiment selects, from the observed light, alight component having a wavelength that is a main part of various lightcomponents composing the incident light L.

The detecting device 21 is configured by a light receiving element suchas a CCD. An imaging plane 21 a, which is an image pickup planeconfigured by a light receiving surface of the light receiving elementis disposed to face the lens 20. In other words, the detecting device 21detects, over the imaging plane 21 a, light intensity information of theincident light L in a state in which imaging is carried out by the lens.

The lens 20 is a convex lens. When the incident light L is incident onthe lens 20, therefore, a transmitted light refracted to be collected isemitted from the lens 20. The light emitted from the lens forms an imageon an imaging point F. In the present embodiment, an advancing directionX1 of the incident light L is inclined by a inclination angle θa withrespect to an optical axis of the lens 20. In other words, an opticalaxis AX of the lens 20 has a different orientation from the advancingdirection X1 of the incident light L. In other words, a main plane TX ofthe lens 20 is inclined by the inclination angle θa with respect to aperpendicular surface to the advancing direction X1 of the incidentlight L. The main plane TX of the lens 20 is a surface that passesthrough a main point PP of the lens 20 and is perpendicular to theoptical axis AX of the lens 20. The main plane TX of the lens 20 passesthrough a center in a vertical direction of the lens 20. The lens 20 canbe designed by a known lens designing technique.

The incident angle of each position component of the incident light L,which is incident on each position over a surface of the lens 20, is notrotationally symmetrical with respect to the optical axis AX of the lens20 because of the presence of the inclination angle θa of the lens 20.In other words, the position component of the incident light L isincident on the lens 20 at an incident angle that is non-rotationallysymmetrical. Accordingly, the position component of the incident light Lis refracted in each lens 20 portion at a refraction angle that isnon-rotationally symmetrical with respect to the optical axis AX of thelens 20. Therefore, the imaging point F is not present on an extendedline LX in the advancing direction X1 from the main point PP of the lens20. The imaging point F is present apart from the extended line LX.

For this reason, when the incident light L is incident on the lens 20inclined with respect to the advancing direction X1, it is refracted ata refraction angle that is non-rotationally symmetrical for each portionof the lens 20. In other words, light L10 emitted from the lens 20advances in a different orientation from the advancing direction X1 of afar incident light L1 and an image is thus formed on the imaging pointF.

The lens 20 has a property having a refractive index that is varied foreach wavelength of the light, that is, so-called chromatic aberration.For this reason, light components having respective wavelengths in thelight L10 emitted from the lens 20 are emitted from the lens 20 indifferent orientations from each other at refractive indicescorresponding to the respective wavelengths. In other words, the lightL10 is emitted at a non-rotationally symmetrical refraction angle basedon the refractive indices, which are different from each other for eachwavelength of the light, and advances in an orientation corresponding toeach of the refraction angles so that an image is formed on the imagingpoint F in different positions from each other. More specifically, theimaging points F for lights having respective wavelengths are formed indifferent positions from each other for each wavelength of the incidentlight L over the common imaging plane 21 a.

The imaging point F for a short wavelength and the imaging point F for along wavelength do not always carry out imaging on the common imagingplane 21 a but it can be supposed that an axial chromatic aberration isalso generated slightly. In the present embodiment, however, theinclination angle θa, a range of an object distance s, which is thedistance to a measuring target, a material of the lens 20 and arefractive index are preset in such a manner that the axial chromaticaberration is included within a range of a focal depth as compared withthe difference between positions of the imaging point F for the shortwavelength and the imaging point F for the long wavelength over thesingle imaging plane 21 a, that is, a shift amount. In other words, itis assumed that the axial chromatic aberration can be disregarded ascompared with the shift amount of an imaging position in a horizontaldirection or a vertical direction of the lens 20.

FIGS. 3(a) to 3(c) are views for explaining a relationship between animaging position and an object distance s, which is the distance fromthe spectrum sensor 14 to a measuring target T. FIG. 3(a) shows the caseof a far measuring target T1 in which a measuring target is present in adistant place. FIG. 3(b) shows the case of a middle measuring target T2in which the measuring target is present closer to the lens 20 than inthe case of FIG. 3(a). FIG. 3(c) shows the case of a near measuringtarget T3 in which the measuring target is present closer to the lens 20than in the case of FIG. 3(b).

FIG. 3(a) shows the far measuring target T1 present at a far objectdistance s1 which can be evaluated as an infinite distance from the lens20. In this case, far incident light L1, which is incident light fromthe far measuring target T1, is incident as almost parallel light in theadvancing direction X1 on the lens 20. If the far incident light L1 is asingle wavelength of light having only light of a short wavelength,which is a first wavelength, for example, a wavelength of 400 nm, whichis refracted based on a refractive index of the lens 20 corresponding tothe wavelength of 400 nm and a refractive index corresponding to theinclination angle θa of the lens 20 and is emitted as a far shortemitted light L11 from the lens 20. The far short emitted light L11carries out imaging at a far short imaging point F11 on the imagingplane 21 a.

On the other hand, if the far incident light L1 is a single wavelengthlight having only light of a long wavelength that is a secondwavelength, which is different from the short wavelength, for example, awavelength of 800 nm, it is refracted based on a refractive index of thelens 20, which corresponds to the wavelength of 800 nm, and a refractiveindex corresponding to the inclination angle θa of the lens 20 and isemitted as a far long emitted light L12 from the lens 20. An image ofthe far long emitted light L12 is formed on a far long imaging point F12over the imaging plane 21 a. In the case of a lens that is not subjectedto a chromatic aberration correction, generally, the refractive indextends to be increased with a reduction in the wavelength. As shown inFIG. 3(a), consequently, the refraction of the far short emitted lightL11 having a short wavelength (a wavelength of 400 nm) is higher thanthe refraction of the far long emitted light L12 having the longwavelength of 800 nm. Accordingly, the position of the far long imagingpoint F12 of the far long emitted light L12 is different from that ofthe far short imaging point F11 of the far short emitted light L11 overthe common imaging plane 21 a. The far short imaging point F11 ispositioned in a more distant place than a place in which the far longimaging point F12 is positioned with respect to the extended line LX inthe advancing direction X1, which passes through the main point PP ofthe lens 20. In FIG. 3(a), the far short imaging point F11 is positionedin a lower place than a place in which the far long imaging point F12 ispositioned. For this reason, a far shift amount D1 (D1=the position ofthe far short imaging point F11−the position of the far long imagingpoint F12) is generated in a vertical direction, for example, as a shiftamount, which is the quantity of a relative relationship, that is, animaging relative quantity due to a shift of an imaging position that iscaused by the difference in a wavelength between the position of the farshort imaging point F11 of the far short emitted light L11 and that ofthe far long imaging point F12 of the far long emitted light L12. Thefar shift amount D1 represents a distance in a direction perpendicularto the extended line LX in the advancing direction X1, which passesthrough the main point PP of the lens 20.

FIG. 3(b) shows a middle measuring target T2 positioned at a middleobject distance s2 in which the distance from the lens 20 is smallerthan the far object distance s1. A middle expansion angle θ2 shown inFIG. 3(b) indicates an expansion angle representing a degree at which amiddle incident light L2, which is an incident light in this case,expands from the measuring target T toward a peripheral edge portion ofthe lens 20, that is, an intake angle. When the expansion angle isincreased, the incident angle on the lens 20 is increased. A farexpansion angle θ1, which is an expansion angle in the case of FIG.3(a), is almost zero. In a case in which the middle incident light L2from the middle measuring target T2 is a single wavelength light havinga short wavelength of 400 nm, the middle incident light L2 is refractedbased on a refractive index of the lens 20 corresponding to a shortwavelength, a refraction angle obtained by an inclination angle θa ofthe lens 20, and a refraction angle obtained by the middle expansionangle θ2 toward the lens 20. An image of a middle short emitted lightL21 emitted from the lens 20 in this case is formed on a middle shortimaging point F21 over an imaging plane 21 a that is almost the same asthat in the case of FIG. 3(a).

On the other hand, if the middle incident light L2 is a singlewavelength light having a long wavelength of 800 nm, the middle incidentlight L2 is refracted based on a refractive index of the lens 20 thatcorresponds to a long wavelength, a refraction angle obtained by theinclination angle θa of the lens 20, and a refraction angle defined bythe middle expansion angle θ2 toward the lens 20. An image of a middlelong emitted light L22 emitted from the lens 20 is formed on a middlelong imaging point F22 over almost the same imaging plane 21 a. Sincethe lens 20 is not subjected to the chromatic aberration correction, therefraction of the middle short emitted light L21 having the shortwavelength of 400 nm is higher than that of the middle long emittedlight L22 having the long wavelength of 800 nm as shown in FIG. 3(b).Accordingly, the position of the middle long imaging point F22 of themiddle long emitted light L22 is different from that of the middle shortimaging point F21 of the middle short emitted light L21 over the commonimaging plane 21 a. For this reason, a middle shift amount D2 (D2=theposition of the middle short imaging point F21−the position of themiddle long imaging point F22) is generated in a vertical direction, forexample, as a quantity of a relative relationship due to a shift of animaging position that is caused by the difference in wavelength betweenthe position of the middle short imaging point F21 of the middle shortemitted light L21 and that of the middle long imaging point F22 of themiddle long emitted light L22. The refraction angle obtained by theinclination angle θa of the lens 20 and the refraction angle defined bythe middle expansion angle θ2 toward the lens 20 indicate anon-rotationally symmetrical refraction angle of the lens 20.

FIG. 3(c) shows a near measuring target T3, which is present at a nearobject distance s3, which is a shorter distance from the lens 20 thanthe middle object distance s2. A near expansion angle θ3 shown in FIG.3(c) is greater than the middle expansion angle θ2 in FIG. 3(b). In acase in which a near incident light L3 from the near measuring target T3is a single wavelength light having a short wavelength of 400 nm, thenear incident light L3 is refracted based on the refractive index of thelens 20 corresponding to the short wavelength, the refraction angleobtained by the inclination angle θa of the lens 20, and a refractionangle defined by the near expansion angle θ3 toward the lens 20. Animage of near short emitted light L31 emitted from the lens 20 is formedon a near short imaging point F31 over almost the same imaging plane 21a.

On the other hand, if the near incident light L3 is single wavelengthlight having a long wavelength of 800 nm, the near incident light L3 isrefracted based on a refractive index of the lens 20 that corresponds toa long wavelength, a refraction angle obtained by the inclination angleθa of the lens 20, and a refraction angle defined by the near expansionangle θ3 toward the lens 20. For example, an image of a near longemitted light L32 emitted from the lens 20 is formed on a near longimaging point F32 over almost the same imaging plane 21 a. Since thelens 20 is not subjected to the chromatic aberration correction, therefraction of the near short emitted light L31 having the shortwavelength of 400 nm is higher than that of the near long emitted lightL32 having the long wavelength of 800 nm as shown in FIG. 3(c).Accordingly, the position of the near long imaging point F32 over theimaging plane 21 a is different from that of the near short imagingpoint F31. For this reason, a near shift amount D3 (D3=the position ofthe near long imaging point F32−the position of the near short imagingpoint F31) is generated in a vertical direction as a quantity of arelative relationship, which is a shift of an imaging position that iscaused by the difference in wavelength between the position of the nearshort imaging point F31 and that of the near long imaging point F32.

In general, the refraction angle of the lens 20 with respect to theincident light having a short wavelength depends on the difference inthe incident angle. That is, the refraction angle of the far objectdistance s1 with respect to the far incident light L1, the refractionangle of the middle object distance s2 with respect to the middleincident light L2 and the refraction angle of the near object distances3 with respect to the near incident light L3 are different from eachother. Similarly, the refraction angle of the lens 20 with respect tothe incident light having a long wavelength depends on the difference inthe incident angle. That is, the refraction angle of the far objectdistance s1 with respect to the far incident light L1, the refractionangle of the middle object distance s2 with respect to the middleincident light L2 and the refraction angle of the near object distances3 with respect to the near incident light L3 are different from eachother.

Moreover, a relative relationship such as the ratio of thenon-rotationally symmetrical refraction angle of the lens 20 withrespect to the incident light having a short wavelength to thenon-rotationally symmetrical refraction angle of the lens 20 withrespect to the incident light having a long wavelength to the far objectdistance s1 is not usually coincident with a relative relationship suchas the ratio of the non-rotationally symmetrical refraction angle of thelens 20 with respect to the incident light having a short wavelength tothe non-rotationally symmetrical refraction angle of the lens 20 withrespect to the incident light having a long wavelength to the middleobject distance s2. Furthermore, a relative relationship such as theratio of the non-rotationally symmetrical refraction angle of the lens20 with respect to the incident angle having a short wavelength to thenon-rotationally symmetrical refraction angle of the lens 20 withrespect to the incident light having a long wavelength to the middleobject distance s2 is not usually coincident with a relativerelationship such as the ratio of the non-rotationally symmetricalrefraction angle of the lens 20 with respect to the incident lighthaving a short wavelength to the non-rotationally symmetrical refractionangle of the lens 20 with respect to the incident light having a longwavelength to the near object distance s3. In addition, the relativerelationship such as the ratio of the non-rotationally symmetricalrefraction angle of the lens 20 with respect to the incident lighthaving a short wavelength to the non-rotationally symmetrical refractionangle of the lens 20 with respect to the incident light having a longwavelength to the far object distance s1 is not usually coincident withthe relative relationship such as the ratio of the non-rotationallysymmetrical refraction angle of the lens 20 with respect to the incidentlight having a short wavelength to the non-rotationally symmetricalrefraction angle of the lens 20 with respect to the incident lighthaving a long wavelength to the near object distance s3.

Accordingly, the far shift amount D1 in the case of the far objectdistance s1 to the far measuring target T1, the middle shift amount D2in the case of the middle object distance s2 to the middle measuringtarget T2, and the near shift amount D3 in the case of the near objectdistance s3 to the near measuring target T3 are different from eachother. For this reason, in the spectrum measuring apparatus 11, it canbe concluded that the far shift amount D1 corresponds to the far objectdistance s1, the middle shift amount D2 corresponds to the middle objectdistance s2, and the near shift amount D3 corresponds to the near objectdistance s3. In other words, it can be concluded that the objectdistance s and the shift amount D have a unique correspondingrelationship in the spectrum measuring apparatus 11. Accordingly, thespectrum measuring apparatus 11 can measure the object distance s to bethe distance to the measuring target T by using chromatic aberration ofmagnification.

As shown in FIG. 4, it is assumed that a pedestrian T3, the othervehicle T2 and a tree T1 are present as measuring targets at a shortdistance, a middle distance and a long distance in the image pickupregion of the spectrum sensor 14, respectively. As shown in FIG. 4(a), ashort wave image P1 in which the far incident light L1 having a shortwavelength of 400 nm is projected onto the imaging plane 21 a in thiscase includes a short wave pedestrian image T31, which is an image ofthe pedestrian T3, a short wave other vehicle image T21, which is animage of the other vehicle T2, and a short wave tree image T11, which isan image of the tree T1.

On the other hand, as shown in FIG. 4(b), a long wave image P2 in whichthe far incident light L1 having a long wavelength of 800 nm isprojected onto the imaging plane 21 a includes a long wave pedestrianimage T32, which is the image of the pedestrian T3, a long wave othervehicle image T22, which is the image of the other vehicle T2, and along wave tree image T12, which is the image of the tree T1.

In other words, the actual object of the short wave pedestrian image T31of the short wave image P1 is the pedestrian T3, which is the same asthe actual object of the long wave pedestrian image T32 of the long waveimage P2. The actual object of the short wave other vehicle image T21 ofthe short wave image P1 is the other vehicle T2, which is the same as anactual object of the long wave other vehicle image T22 of the long waveimage P2. The actual object of the short wave tree image T11 of theshort wave image P1 is the tree T1, which is the same as an actualobject of the long wave tree image T12 of the long wave image P2.

A third detecting region W3 for comparing an imaging position of thepedestrian T3 for each wavelength, a second detecting region W2 forcomparing an imaging position of the other vehicle T2 for eachwavelength and a first detecting region W1 for comparing an imagingposition of the tree T1 for each wavelength are set to the short waveimage P1 and the long wave image P2, respectively. With respect to theimaging plane 21 a, the position of the third detecting region W3 of theshort wave image P1 is set to be identical to the position of the thirddetecting region W3 of the long wave image P2. With respect to theimaging plane 21 a, similarly, the position of the second detectingregion W2 of the short wave image P1 is set to be identical to theposition of the second detecting region W2 of the long wave image P2.With respect to the imaging plane 21 a, the position of the firstdetecting region W1 of the short wave image P1 is set to be identical tothe position of the first detecting region W1 of the long wave image P2.

As described above, the spectrum sensor 14 according to the presentembodiment changes an imaging position of a measuring target between theshort wavelength of 400 nm and the long wavelength of 800 nm.Consequently, in a case in which the distance to the pedestrian T3 isthe near object distance S3, for example, the near shift amount D3 isgenerated in a vertical direction between the position of the short wavepedestrian image T31 and that of the long wave pedestrian image T32 inthe imaging plane 21 a. Moreover, in a case in which the distance to theother vehicle T2 is the middle object distance s2, for example, themiddle shift amount D2 is generated in the vertical direction betweenthe position of the short wave other vehicle image T21 and the positionof the long wave other vehicle image T22 in the imaging plane 21 a. Inaddition, in a case in which the distance to the tree T1 is the farobject distance s1, for example, the far shift amount D1 is generated inthe vertical direction between the position of the short wave tree imageT11 and the position of the long wave tree image T12 in the imagingplane 21 a.

In other words, the spectrum sensor 14 can determine that the distanceto the pedestrian T3 is the near object distance s3 based on the factthat the shift between the position of the short wave pedestrian imageT31 and that of the long wave pedestrian image T32 is equal to the nearshift amount D3. Moreover, the spectrum sensor 14 can determine that thedistance to the other vehicle T2 is the middle object distance s2 basedon the fact that the shift between the position of the short wave othervehicle image T21 and that of the long wave other vehicle image T22 isequal to the middle shift amount D2. Furthermore, the spectrum sensor 14can determine that the distance to the tree T1 is the far objectdistance s1 based on the fact that the shift between the position of theshort wave tree image T11 and that of the long wave tree image T12 isequal to the far shift amount D1. More specifically, the spectrum sensor14 can grasp the object distance s from a shift amount, that is, thedifference between an imaging position of an image based on a shortwavelength of the measuring target and that of an image based on a longwavelength of the measuring target in the imaging plane 21 a.

As shown in FIG. 1, the spectrum sensor 14 thus detects the spectraldata R0 configured by the short wave image P1, which is a spectral imagebased on a short wavelength, and the long wave image P2, which is aspectral image based on a long wavelength, with respect to the measuringtarget T. Then, the spectrum sensor 14 outputs the spectral data R0 tothe spectral data processing device 15.

The spectral data processing device 15 is mainly configured by amicrocomputer having a computation device, a storage unit and the like,for example. The spectral data processing device 15 is connected to thespectrum sensor 14, and furthermore, the spectral data R0 of theobserved light detected by the spectrum sensor 14 is input to thespectral data processing device 15. The spectral data processing device15 calculates, that is, measures the object distance s based on thespectral data R0 of the observed light input thereto.

The spectral data processing device 15 includes a computation device 16and a storage unit 17 serving as storage means. The storage unit 17 isconfigured by a whole or part of a storage area provided in thewell-known storage device.

FIG. 5 shows an example of map data 18 stored in the storage area. Themap data 18 indicates the shift amount (D1, D2, D3 or the like), whichis the difference between the imaging position of the light having theshort wavelength and the imaging position of the light having the longwavelength in such a manner as to be related to the object distance s(s1, s2, s3 or the like), which is the distance to the measuring targetT. In other words, the map data 18 stores the far shift amount D1, whichis the difference between the position of the far short imaging pointF11 and that of the far long imaging point F12 in relation to the farobject distance s1 to the far measuring target T1. Furthermore, the mapdata 18 stores the middle shift amount D2, which is the differencebetween the position of the middle short imaging point F21 and that ofthe middle long imaging point F22 in relation to the middle objectdistance s2 to the middle measuring target T2. In addition, the map data18 stores the near shift amount D3, which is the difference between theposition of the near short imaging point F31 and that of the near longimaging point F32 in relation to the near object distance s3 to the nearmeasuring target T3. Accordingly, the computation device 16 can acquire,from the map data 18, the long object distance s1 based on the far shiftamount D1, the middle object distance s2 based on the middle shiftamount D2 or the near object distance s3 based on the near shift amountD3. In other words, the map data 18 constitutes correlation information,which is information determined by the chromatic aberrationcharacteristic of the lens 20 and the orientation of the optical axis AXin order to indicate a correlation between the shift amount D, which isan imaging relative quantity and the object distance s.

The computation device 16 includes a noted image selecting unit 30 forselecting any of the images of the measuring target T that will be usedfor measuring a distance; an imaging position calculating unit 31 fordetecting imaging positions for two wavelengths from the selected image;and a shift amount calculating unit 32 for calculating the shift amountD, which is the difference between the imaging positions for twowavelengths. Furthermore, the computation device 16 includes a distancecalculating unit 33 serving as distance calculating means forcalculating the object distance s from the shift amount D. The imagingposition calculating unit 31 and the shift amount calculating unit 32constitute imaging relative quantity calculating means serving asrelative relationship quantity calculating means.

The noted image selecting unit 30 selects any of the images of themeasuring target T that will be used for measuring a distance on a pixelunit. When inputting the spectral data R0 from the spectrum sensor 14,the noted image selecting unit 30 outputs, to the imaging positioncalculating unit 31, noted image information W0 and spectral data R1including spectral images for two wavelengths. The noted image selectingunit 30 may select an image corresponding to a measuring target having ahigh priority from the recognized measuring targets based on an objectrecognition processing carried out separately or may select an imagecorresponding to a measuring target occupying a large number of areaswhen the image is to be selected. Moreover, it is preferable that theimage to be selected by the noted image selecting unit 30 should be aboundary portion with a background or the like in order to enable anidentification of positions of images having two wavelengths which aredifferent from each other, respectively.

FIG. 4(a) shows the short wave image P1, which is an image having ashort wavelength, and FIG. 4(b) shows the long wave image P2 which is animage having a long wavelength. It is assumed that the far measuringtarget T1 is a “tree”, the middle measuring target T2 is “the othervehicle” and the near measuring target T3 is a “pedestrian”. The shortwave image P1 in FIG. 4(a) indicates the short wave tree image T11,which is an image of the tree, the short wave other vehicle image T21,which is an image of the other vehicle, and the short wave pedestrianimage T31, which is an image of the pedestrian. The long wave image P2in FIG. 4(b) indicates the long wave tree image T12, which is an imageof the tree, the long wave other vehicle image T22, which is an image ofthe other vehicle, and the long wave pedestrian image T32, which is animage of the pedestrian.

The noted image selecting unit 30 selects a first noted image PX1 fromthe short wave tree image T11 and the long wave tree image T12 in a casein which the tree T1 is the measuring target. The noted image selectingunit 30 sets the first detecting region W1 in which both the short waveimage P1 and the long wave image P2 include the first noted image PX1.The first noted image PX1 indicates a boundary line between a bottom ofthe tree T1 and ground provided under the bottom.

Moreover, the noted image selecting unit 30 selects a second noted imagePX2 from the short wave other vehicle image T21 and the long wave othervehicle image T22 in a case in which the other vehicle T2 is themeasuring target. The noted image selecting unit 30 sets the seconddetecting region W2 in which both the short wave image P1 and the longwave image P2 include the second noted image PX2. The second noted imagePX2 includes a boundary line between a tire of the other vehicle T2 anda road surface provided under the tire.

Furthermore, the noted image selecting unit 30 selects a third notedimage PX3 from the short wave pedestrian image T31 and the long wavepedestrian image T32 in a case in which the pedestrian T3 is themeasuring target, for example. In addition, the noted image selectingunit 30 sets the third detecting region W3 in which both the short waveimage P1 and the long wave image P2 include the third noted image PX3.The third noted image PX3 includes a boundary line between shoes of thepedestrian T3 and the road surface provided under the shoes.

In other words, the noted image selecting unit 30 generates the notedimage information W0 including the first noted image PX1 and the firstdetecting region W1, the second noted image PX2 and the second detectingregion W2, and the third noted image PX3 and the third detecting regionW3, and outputs the noted image information W0 to the imaging positioncalculating unit 31.

The imaging position calculating unit 31 detects imaging positions forimages having two wavelengths respectively based on the noted imageselected by the noted image selecting unit 30. The imaging positioncalculating unit 31 inputs the noted image information W0 and thespectral data R1 from the noted image selecting unit 30, andfurthermore, calculates the imaging positions for two wavelengths of thenoted image based on the noted image information W0 and the spectraldata R1. Then, the imaging position calculating unit 31 outputs, to theshift amount calculating unit 32, the imaging position data R2 includingthe imaging positions for the calculated two wavelengths.

The shift amount calculating unit 32 calculates the shift amount D fromthe imaging positions for the two wavelengths. The shift amountcalculating unit 32 calculates, as the shift amount D, the differencebetween the imaging positions for the two wavelengths (for example, theposition of the far short imaging point F11 and the position of the farlong imaging point F12) based on the imaging position data R2 input fromthe imaging position calculating unit 31. The shift amount calculatingunit 32 outputs the calculated shift amount D as shift amount data R3,which is data related to the two wavelengths to the distance calculatingunit 33.

The distance calculating unit 33 calculates the object distance s basedon the shift amount data R3. In other words, the distance calculatingunit 33 selects, from the storage unit 17, the map data 18 correspondingto the two wavelengths (for example, 400 nm and 800 nm) acquired fromthe shift amount data R3 based on the two wavelengths. Then, thedistance calculating unit 33 acquires, from the selected map data 18,the object distance s (for example, the far object distance s1)corresponding to the shift amount acquired from the shift amount data R3(for example, the far shift amount D1). The distance calculating unit 33generates distance data R4 by relating the acquired object distance s tothe measuring target T, for example, and outputs the distance data R4 tothe human machine interface 12, the vehicle control device 13 and thelike.

FIG. 6 explains a procedure for measuring the object distance s. FIG. 6is a flowchart showing the procedure for measuring the object distance sby the spectrum measuring apparatus 11 according to the presentembodiment. In the present embodiment, the procedure for measuring theobject distance s is successively executed in a predetermined cycle.

As shown in FIG. 6, when processing for measuring distance is started,the computation device 16 acquires the spectral data R0 detected by thespectrum sensor 14 at Step S10. When acquiring the spectral data R0, thecomputation device 16 selects a noted image from the images of themeasuring target T of which distance is to be measured at Step S11. Themeasuring target T is selected by setting, as a condition, a measuringtarget recognized separately by the spectrum measuring apparatus 11, apriority of the measuring target or the like. When the noted image isselected, the computation device 16 calculates an imaging position ofthe noted image for each of short and long wavelengths to be used formeasuring a distance at Step S12 (an imaging position calculating step).The imaging position is obtained based on the position of the pixel onthe imaging plane 21 a in which the noted image is to be detected. Whenthe imaging position is calculated, the computation device 16 comparesthe positions of the noted images for the two wavelengths with eachother, thereby calculating the shift amount D to be an imaging relativequantity at Step S13 (an imaging relative quantity calculating step).The shift amount D (D1, D2, D3) is calculated as the difference betweenthe imaging positions of the respective noted images having the twowavelengths. When calculating the shift amount D, the computation device16 calculates the object distance s at Step S14 (a distance calculatingstep). The computation device 16 calculates the object distance s byacquiring the distance corresponding to the shift amount D from the mapdata 18 corresponding to the two wavelengths.

As described above, according to the spectrum measuring apparatus 11 inaccordance with the present embodiment, it is possible to obtain thefollowing listed advantages.

(1) The spectrum measuring apparatus 11 uses the lens 20 having theoptical axis AX in the orientation different from the advancingdirection X1 of the incident light L so that the imaging positions forthe respective wavelengths are different from each other. Consequently,the imaging relative quantity between the imaging positions is detectedas a quantity that is varied for each object distance s. In other words,the spectrum measuring apparatus 11 can measure the object distance sbased on the imaging relative quantities, which are different from eachother. An ordinary lens has a refractive index that is varied for eachlight having a different wavelength, that is, causes chromaticaberration. For this reason, when the lens 20 carries out imaging overlights having a plurality of wavelengths, the imaging position is variedfor each light having a different wavelength. In a case in which theoptical axis AX of the lens 20 is inclined with respect to the advancingdirection X1 of the far incident light L1, that is, the case in whichthe lens 20 refracts the far incident light L1 in the orientation of theoptical axis AX thereof, consequently, the lights having the respectivewavelengths are refracted in the respective refractive indices.Accordingly, the imaging position of the image formed by the lens 20(the position of the imaging point) is displaced in different quantitiesfrom each other in a horizontal direction or a vertical direction of thelens 20 for each light having a different wavelength. On the other hand,when the incident angle of the light on the lens 20 is varied dependingon a change in the object distance s between the lens 20 and themeasuring target T, the imaging position of light of a single wavelengthis also changed. Consequently, the spectrum measuring apparatus 11 canmeasure the object distance s based on a relative relationship betweenthe imaging positions for the respective wavelengths.

(2) The imaging positions for the respective wavelengths are varied inthe horizontal direction or the vertical direction of the lens 20. Inother words, the imaging positions for the respective wavelengths aredisplaced in different quantities from each other in a directionperpendicular to the advancing direction X1 of the incident light L.Consequently, images for the respective wavelengths are formed on theimaging plane 21 a, which is generally provided to face the lens 20.Accordingly, the imaging plane 21 a can detect the respective imagingpositions of the images of the lights having the respective wavelengths.In other words, the spectrum measuring apparatus 11 does not need tomove the imaging plane 21 a in order to detect the imaging position. Forthis reason, a device for moving the imaging plane 21 a is not required.Thus, the imaging positions for the respective wavelengths can bedetected with a simple structure.

(3) By detecting the imaging positions for the respective wavelengthsthrough the same lens 20 (the optical system), it is possible to obtainthe difference between the imaging positions for the respectivewavelengths based on the chromatic aberration. In other words, thedistance can be measured by means of a single optical system, that is, asingle camera (the spectrum sensor 14). Therefore, as compared with thecase in which a plurality of cameras is used, for example, theflexibility of the arrangement of the camera can be enhanced in thepresent embodiment. In other words, the arranging position of the cameradoes not need to be maintained with high precision but the structure ofthe distance measuring apparatus can be simplified.

(4) An ordinary lens is subjected to a chromatic aberration correction.In other words, the ordinary lens is often configured in such a mannerthat the imaging distances of the lights having the respectivewavelengths are coincident with each other for only lights havingwavelengths to be acquired, for example, only lights having a redwavelength, a blue wavelength and a green wavelength for an image. Inthe present embodiment, however, it is possible to use, for themeasurement of the distance, the lens 20 which is not subjected to thechromatic aberration correction. Accordingly, it increases theflexibility of the selection and a design of a wavelength to be used inthe distance measuring apparatus, and furthermore, it also increases theflexibility of the selection and a design of the optical system to beemployed for the distance measuring apparatus.

(5) The spectrum measuring apparatus 11 measures the object distance sbased on light having two wavelengths in which the imaging positions(the positions of the imaging (focus) points) through the lens 20 aredifferent from each other. In other words, if the light emitted from themeasuring target T has two wavelengths or more, the distance of themeasuring target T can be measured. Therefore, it is possible to easilycarry out the measurement of the distance.

(6) The spectrum measuring apparatus 11 detects the imaging relativequantity as the difference between the imaging positions for twowavelengths, that is, the shift amount D (D1, D2, D3). Accordingly, itis possible to easily carry out a calculation related to the detectionor the like.

(7) The spectrum measuring apparatus 11 inclines the optical axis AX ofthe lens 20 with respect to the far incident light L1, thereby makingthe difference between the imaging positions for the lights having therespective wavelengths. The spectrum measuring apparatus 11 measures theobject distance s based on the difference between the imaging positions.For example, in the case of a general convex lens, the lens 20 isdisposed with an inclination to the advancing direction X1 of the farincident light L1. Consequently, it is possible to incline the opticalaxis AX of the lens 20 with respect to the advancing direction X1 of thefar incident light L1. In the present embodiment, thus, it is possibleto simplify the arrangement or mode of the lens 20 in the distancemeasuring apparatus or the characteristic of the lens 20.

(8) By detecting the image for each wavelength of the measuring targetT, which is formed by the lens 20 through the spectrum sensor 14, it ispossible to detect lights having a plurality of optional wavelengths.Accordingly, the flexibility of the selection of the wavelength is high.Consequently, it is also easy to properly select light of a suitablewavelength for measuring a distance depending on the surroundingenvironment, environmental light or the like. Moreover, the spectrumsensor 14 can originally detect light having a plurality of wavelengths.Therefore, the distance measuring apparatus can be configured simply. Inother words, the existing spectrum sensor can also be practically usedas the distance measuring apparatus.

The embodiment may also be carried out in the following modes, forexample.

In the embodiment, there is described the case in which the wavelengthof the light that is incident on the lens 20 is set to be a shortwavelength or a long wavelength by a filter. However, the presentinvention is not restricted thereto but the filter may acquire anemitted light having a predetermined light from the lights emitted fromthe lens 20. Accordingly, it increases the flexibility of the structurefor acquiring light having a predetermined wavelength.

In the embodiment, a combination of the wavelengths of the difference(the shift amount) between the imaging positions, which is stored by themap data 18, includes a short wavelength and a long wavelength. However,the present invention is not restricted thereto but a combination of thewavelengths that is stored by the map data 18 may be any of the othercombinations. The map data 18 may be a plurality of map data based on acombination of different wavelengths from each other. Accordingly, itincreases the flexibility for the selection of a wavelength to be usedfor measuring a distance.

In the embodiment, reference is made to the map data 18 in order tocalculate the object distance s from the shift amount D. However, thepresent invention is not restricted thereto but the object distance smay be calculated from the shift amount D by using an arithmeticexpression. Accordingly, it is possible to reduce the storage area.

In the embodiment, the imaging plane 21 a is disposed to expandperpendicularly to the advancing direction X1 of the incident light L.However, the present invention is not restricted thereto but the imagingplane 21 a may be inclined with respect to the advancing direction X1 ofthe incident light L. For example, in a case in which the imagingdistance f from the lens 20 to the imaging point is varied based on thewavelength of the light or the object distance s, the imaging plane 21 amay be inclined in such a manner that the distance between the imagingplane 21 a portion for picking up an image of the imaging point and thelens 20 is changed. Therefore, it is possible to enhance precision inthe measurement of the distance that is to be carried out by thedistance measuring apparatus.

In the embodiment, the imaging relative quantity is set to be thedifference (the shift amount) between the imaging positions for twowavelengths. However, the present invention is not restricted theretobut the imaging relative quantity may be set to be a ratio of theimaging positions of the lights having the two wavelengths. Thisincreases the flexibility for calculation of the imaging relativequantity in the imaging positions for the two wavelengths. Thus, it ispossible to obtain a suitable result for the measurement.

In the embodiment, the object distance s is calculated based on a singleshift amount. However, the present invention is not restricted theretobut the object distance s may be calculated based on a plurality ofshift quantities including other shift quantities detected by acombination of other wavelengths. Based on the shift quantities, theobject distance s is obtained with high precision. In particular, aspectrum sensor capable of detecting lights having a large number ofwavelengths can detect imaging positions of images for a large number ofwavelengths. In other words, it is possible to calculate a large numberof shift quantities based on the difference between the imagingpositions. Consequently, it is possible to easily measure a distancebased on a large number of shift quantities, and furthermore, to enhanceprecision in the distance to be measured.

In the embodiment, there is described the case in which the lens 20 is asingle convex lens. However, the present invention is not restrictedthereto but it is sufficient that the lens 20 is an optical system forforming an image from incident light. Therefore, the lens 20 may beconfigured by a plurality of lenses. Moreover, the lens 20 may beconfigured to include a concave lens. The flexibility for the design ofthe lens is increased. Consequently, it increases the flexibility forthe employment of the distance measuring apparatus.

In the embodiment, the main plane TX of the lens 20, that is, a centralsurface, which is a surface passing through a center in a verticaldirection of the lens 20, has the inclination angle θa with respect to aperpendicular surface to the advancing direction X1 of the incidentlight L. However, the present invention is not restricted thereto butthe central surface passing through the center in the vertical directionof the lens 20 may be set to be perpendicular to the advancing directionX1 of the incident light L if the optical axis AX of the lens 20 has adifferent orientation from the advancing direction X1 of the incidentlight L. In other words, in a case in which the optical axis AX of thelens 20 has an inclination with respect to the advancing direction X1 ofthe incident light L, the angle of the incident light is varied based onthe object distance s. Accordingly, the imaging position, that is, theposition of the imaging point is displaced in a horizontal direction ora vertical direction over a perpendicular surface to the advancingdirection X1 of the incident light L. Therefore, an imaging relativequantity is generated so that the object distance s can be measured.

As shown in FIG. 7, a surface of a lens 25, which is a convex lens, maybe formed non-rotationally symmetrically. For example, the thickestportion of the lens 25 is inclined from a center of the lens 25. In FIG.7, a maximum thickness of the lens 25 is inclined toward an upper partof the lens 25. For this reason, an optical axis AX is also inclinedupward. In this case, the surface of the lens 25 is non-rotationallysymmetrical with respect to the optical axis AX of the lens 25. In otherwords, the surface of the lens 25 may be made non-rotationallysymmetrical with respect to the optical axis AX, thereby inclining theoptical axis AX of the lens 25 to the advancing direction X1 of theincident light L. Also in this case, an imaging position is varieddepending on the wavelength of the incident light L and the objectdistance s over the imaging plane 21 a. Accordingly, it increases theflexibility for the design or structure of the distance measuringapparatus. A specific structure of the lens 25 in FIG. 7 may be changed.

As shown in FIG. 8, a lens 26, which is a convex lens, may be configuredby a first member 26 a and a second member 26 b, which have differentrefractive indices (aberrations) from each other to incline an opticalaxis AX of the lens 26 with respect to the advancing direction X1 of theincident light L. In FIG. 8, the first member 26 a, which is close tothe measuring target T, is concave in an upper part of the drawing andis convex in a lower part of the drawing with respect to the advancingdirection X1 of the incident light L. The second member 26 b is convexin the upper part of the drawing and is concave in the lower part of thedrawing in order to fill in the concavo-convex portions of the firstmember 26 a. Also in this case, the optical axis AX of the lens 26 isinclined upward. In other words, a refractive index of the lens 26 maybe made non-rotationally symmetrical with respect to the optical axis AXto incline the optical axis AX of the lens 26 with respect to theadvancing direction X1 of the incident light L. Also in this case, animaging position is varied depending on the wavelength of the incidentlight L and the object distance s over the imaging plane 21 a.Accordingly, it also increases the flexibility for the design orstructure of the distance measuring apparatus. A specific structure ofthe lens 26 in FIG. 8 can be changed. Moreover, a single convex lens maybe configured by three members or more.

The lens 25 in FIG. 7 or the lens 26 in FIG. 8 may be disposed in such amanner that a central surface (TX) passing through a center in avertical direction is inclined with respect to the advancing directionX1 of the incident light L. Consequently, it increases the flexibilityfor the design or the structure of the distance measuring apparatus.

In the embodiment, there is described the case in which the lens 20 isnot subjected to chromatic aberration correction. However, the presentinvention is not restricted thereto but the lens may be subjected tochromatic aberration correction if a wavelength to be used in ameasurement of a distance is not subjected to chromatic aberrationcorrection or the degree of correction is low. Also in an apparatususing a lens subjected to chromatic aberration correction, accordingly,it is possible to increase the possibility that the distance measuringapparatus can be employed.

In the embodiment, there is described a case in which the short and longwavelengths in the two wavelengths to obtain the shift amount D (theimaging relative quantity, which is a relative relationship quantity)are 400 nm and 800 nm, respectively. However, the present invention isnot restricted thereto but two wavelengths to obtain the shift amountcan be selected from visible and invisible light if they have such arelationship that chromatic aberration is caused by the lens 20. Inother words, the short wavelength may be smaller or greater than 400 nmand the long wavelength may be smaller or greater than 800 nm.Accordingly, the flexibility for the selection of a wavelength in adistance measuring apparatus can be enhanced and a suitable combinationof the wavelengths for a measurement of a distance can be selected sothat the measurement of distance can also be carried out suitably. Theinvisible light may include ultraviolet rays (near ultraviolet rays) andinfrared rays (containing far infrared rays, middle infrared rays andnear infrared rays).

In the embodiment, there is described a case in which the shift amount Dis reduced when the object distance s is increased. However, the presentinvention is not restricted thereto but it is sufficient that the shiftamount D is varied depending on a change in the object distance s andmay be increased when the distance is increased. In other words, thedifference between the imaging positions (the shift amount) is variouslychanged depending on a relationship between the characteristic of thelens 20 and the selected wavelength. Therefore, it is sufficient to havesuch a relationship that the difference between the imaging positions(the shift amount) and the object distance s can be set as the map data18. Under this condition, the difference between the imaging positionswith respect to the object distance s may be varied in any way.Accordingly, it increases the flexibility for the selection of anoptical system that can be employed for the distance measuringapparatus.

DESCRIPTION OF THE REFERENCE NUMERALS

10 . . . Vehicle, 11 . . . Spectrum Measuring Apparatus, 12 . . . HumanMachine Interface, 13 . . . Vehicle Control Device, 14 . . . SpectrumSensor, 15 . . . Spectral Data Processing Device, 16 . . . ComputationDevice, 17 . . . Storage Unit, 18 . . . Map Data, 20, 25, 26 . . . Lens,21 . . . Detecting Device, 21 a . . . Imaging Plane, 26 a, 26 b . . .Member, 30 . . . Noted Image Selecting Unit, 31 . . . Imaging PositionCalculating Unit, 32 . . . Shift Amount Calculating Unit, 33 . . .Distance Calculating Unit, AX . . . Optical Axis, F, F11, F12, F21, F22,F31, F32 . . . imaging Point, P1 . . . Short Wave Image as SpectralImage, P2 . . . Long Wave Image as Spectral Image, PX1, PX2, PX3 . . .Noted Image, T, T1, T2, T3 . . . Measuring target, TX . . . Main Plane,T31, T32 . . . Image of Pedestrian, T21, T22 . . . Image of OtherVehicle, T11, T12 . . . Image of Tree.

The invention claimed is:
 1. A distance measuring apparatus formeasuring distance to a measuring target by optically detecting themeasuring target, the apparatus comprising: a lens, an optical axis ofwhich has a different orientation from an advancing direction of lightincident from the measuring target, the lens being configured to form animage from the incident light, thereby obtaining an image of themeasuring target; an imaging relative quantity calculator circuitryconfigured to calculate an imaging relative quantity by obtaining animaging position indicative of the position of the image with respect tothe lens for each of a plurality of wavelengths possessed by theincident light, the imaging relative quantity being a quantityindicative of a relative relationship between the imaging positions; astorage configured to store correlation information, which isinformation determined by a chromatic aberration characteristic of thelens and the orientation of the optical axis in order to indicate acorrelation between the imaging relative quantity and an objectdistance; and a distance calculator circuitry configured to calculatethe object distance by checking the imaging relative quantity againstthe correlation information, the distance calculator circuitry isconfigured to measure the distance to the measuring target based on arelative relationship between the imaging positions for the respectivewavelengths, wherein the light is refracted in a refractive index foreach wavelength so that the imaging positions of the light are differentfrom each other in a direction perpendicular to the advancing directionof the incident light for each wavelength, the object distance, which isthe distance between the lens and the measuring target, is varied sothat an incident angle of the light on the lens is made different, theobject distance is varied so that an imaging position of light of asingle wavelength is also changed, the distance calculator circuitry isconfigured to obtain a difference between the imaging positions for therespective wavelengths based on the chromatic aberration by detectingthe imaging positions for the respective wavelengths through a commonlens by using light having a wavelength that is not subjected to thechromatic aberration correction for the measurement of the distance. 2.The distance measuring apparatus according to claim 1, wherein the lighthas two wavelengths, in which the imaging positions are different fromeach other, and the correlation information constitutes map data, inwhich the imaging relative quantities are caused to correspond to theobject distances, respectively.
 3. The distance measuring apparatusaccording to claim 2, wherein the imaging relative quantity is animaging position difference, which is the difference between the imagingpositions for the two wavelengths.
 4. The distance measuring apparatusaccording to claim 2, wherein the imaging relative quantity is animaging position ratio, which is the ratio of the imaging positions forthe two wavelengths.
 5. The distance measuring apparatus according toclaim 1, wherein the optical axis of the lens is inclined with respectto the advancing direction of the incident light.
 6. The distancemeasuring apparatus according to claim 1, wherein a surface of the lensis non-rotationally symmetrical with respect to the optical axis of thelens.
 7. The distance measuring apparatus according to claim 1, whereina refractive index of the lens is non-rotationally symmetrical withrespect to the optical axis of the lens.
 8. The distance measuringapparatus according to claim 1, wherein the lens is a part of a spectrumsensor for detecting light transmitted from the measuring target.
 9. Adistance measuring method using a distance measuring apparatus formeasuring distance to a measuring target by optically detecting themeasuring target, the method comprising: forming an image of themeasuring target by means of a lens of the distance measuring apparatushaving an optical axis in a different orientation from an advancingdirection of light incident from the measuring target; obtaining animaging position indicative of the position of the image with respect tothe lens for each of a plurality of wavelengths possessed by theincident light; using an imaging relative quantity calculator circuitryof the distance measuring apparatus, calculating an imaging relativequantity, which is a quantity indicative of a relative relationshipbetween the imaging positions; using a distance calculator circuitry ofthe distance measuring apparatus, calculating an object distance bychecking the imaging relative quantity against correlation information,which is information determined by the imaging relative quantity, achromatic aberration characteristic of the lens, and the orientation ofthe optical axis in order to indicate a correlation between the imagingrelative quantity and the object distance; using the distance calculatorcircuitry, measuring the distance to the measuring target based on arelative relationship between the imaging positions for the respectivewavelengths, wherein the light is refracted in a refractive index foreach wavelength so that the imaging positions of the light are differentfrom each other in a direction perpendicular to the advancing directionof the incident light for each wavelength, the object distance, which isthe distance between the lens and the measuring target, is varied sothat an incident angle of the light on the lens is made different, theobject distance is varied so that an imaging position of light of asingle wavelength is also changed; and using the distance calculatorcircuitry, obtaining a difference between the imaging positions for therespective wavelengths based on the chromatic aberration by detectingthe imaging positions for the respective wavelengths through a commonlens by using light having a wavelength that is not subjected to thechromatic aberration correction for the measurement of the distance. 10.The distance measuring method according to claim 9, wherein the incidentlight has two wavelengths, the method further comprising: by obtainingan imaging position, obtaining the imaging position for each of the twowavelengths; and acquiring the correlation information from map data,which causes the imaging relative quantity to correspond to the objectdistance to calculate the object distance.